Pressureless Sintering of Zirconium Diboride Ceramics with Boron Additive
Influence of boron on densification and microstructure of zirconium diboride ( ZrB 2) ceramics using pressureless sintering has been studied. The ZrB 2 powders were synthesized
by borothermal reduction of ZrO 2 with three different ZrO 2/ B ratios to produce powders nominally phase pure or that contained excess boron.
The as‐synthesized powders were then densified by heating to temperatures from 1800°C to 2200°C. The incorporation of 1.2 wt% excess boron increased relative density from ~54.3% to ~96.1% by reacting with and removing oxide impurities ( ZrO
2 and B 2 O 3) after sintering at 2000°C, whereas it also led to an exaggerated grain growth from 1–3 to 20–80 μm presumably due to high
grain‐boundary mobility. The faster grain growth resulted in the formation of intragranular pores and prevented the ZrB 2 ceramics from reaching full density. By the incorporation of 3 wt% excess boron, a fully dense
ZrB 2 ceramics with relative density of ~99.7% and grain size of 5–10 μm was obtained at 2000°C. The full densification was attributed to the synergistic effects of boron through oxide impurities removal and grain‐ growth